Graphene-doped electrochemical copolymer coating of 2,2-bithiophene and 3-methylthiophene for the highly effective solid-phase microextraction of volatile benzene homologues

We report the electrochemical fabrication of a poly(2,2-bithiophene-co-3-methylthiophene)-graphene composite coating and its application in the headspace solid-phase microextraction and gas chromatography determination of benzenes (i.e., bromobenzene, 4-bromotoluene, 2-nitrotoluene, 3-nitrotoluene and 1,2,4-trichlorobenzene). The coating was uniform and showed cauliflower-like microstructure. It had high thermal stability (up to 375°C) and could be used for at least 180 times of solid-phase microextraction without a decrease in extraction performance. Furthermore, it presented high extraction capacity for the benzenes due to the hydrophobic effect and π–π interaction between the analytes and the coating. Under optimized extraction conditions, good linearity (correlation coefficients higher than 0.9946), wide linear range (0.01–50 μg/L), and low limits of detection (5.25–12.5 ng/L) were achieved for these analytes. The relative standard deviation was lower than 5.7% for five successive measurements with one fiber, and the relative standard deviation for fiber-to-fiber was 4.9–6.8% ( n = 5). The solid-phase microextraction and gas chromatography method was successfully applied for the determination of three real samples, and the recoveries for standards added were 89.6–106% for nail polish, 85.8–110% for hair dye, and 90–106.2% for correction fluid, respectively.